1. Field of the Invention
The present invention relates to a resin transfer molding process and apparatus, and, in particular, relates to the vacuum assisted resin transfer molding (VARTM) process and apparatus, and further relates to the manufacturing of fiber reinforced resin composite structures, components, and devices therefrom.
2. Description of Related Art
The vacuum assisted resin transfer (VARTM) process and apparatus associated with the present invention provide a low cost organic matrix fiber reinforced composite manufacturing process for constructing structures, components, and devices therefrom.
In the VARTM process, a tool or mold is constructed having a desired shape, for example, with a female mold as may be used in making panels, boat hulls, etc. The mold normally has a single side upon which a preform is placed. The preform may be a combination of one or more layers of mat and/or cloth fabric material, cut in a desired pattern, stacked to a desired depth, and placed on the tool or mold. The fabric material may be composed of glass fibers, carbon graphite fibers, aramid fibers and the like. A release film being conventional and pervious to the selected resin is applied over the preform to ease the separation of the vacuum bag and the preform after the resin has been cured. The mold itself may be Teflon coated or may be coated with a wax or release agent to allow ease of separation of the cured product therefrom. Typically, a conventional distribution medium layer is placed on the release film and provides for a uniform flow of resin into the preform to reduce the formation of voids and other defects which may cause delamination or other structural imperfections. The distribution medium layer may be a non-swelling, non-resin absorptive, open weave fabric knitted to provide a network of close, adjoining or communicating openings, both in the vertical direction and horizontal directions. The resin from the resin source is drawn into the preform assembly by vacuum through flexible tubing. The tubing end may be directly connected into the vacuum bag, acting as a point source, or may be connected into a distribution device such as a coil spring or channel, acting as a line source, to assist in the delivery of the resin to the distribution medium. The vacuum outlets may similarly be connected into the preform assembly as the resin inlets. The resin inlets and vacuum outlets are typically placed on “opposing sides” of the preform since the vacuum draws the resin across and into the preform. As determined by the shape and size of the preform and resin viscosity, resin inlets being either a point or line source and vacuum outlets being either a point or a line source are positioned about the preform so as to insure that all areas of the preform are fully saturated. External resin reservoir(s), a feed source, and a vacuum system are connected by lines such as plastic tubing to the appropriate points and/or lines. The vacuum bag or bags are placed over the above items and sealed to the tool to form an interior chamber in the preform assembly for drawing a vacuum. A vacuum is created by the vacuum system in the interior chamber formed between the mold and the vacuum bag which draws the resin into the chamber, into the distribution medium layer, into the preform and finally into a resin trap during the VARTM process. During a typical the VARTM process, a low pressure to high pressure gradient is created between the resin inlets and the vacuum outlets. After the preform is fully impregnated as determined by sight or sensors, the resin with catalyst therein is allowed to cure either at room temperature or at an elevated temperature to accelerate the curing after which the vacuum bag, the distribution medium layer, the release film, and the preform are removed from the mold. At this point the preform with cured resin therein is ready for further manufacturing steps to produce a final structure, component, or device that may be used by itself or incorporated into another structure.
U.S. Pat. No. 4,902,215 by inventor Seemann, III, entitled “Plastic Transfer Molding Techniques for the Production of Fiber Reinforced Plastic Structures” discloses the VARTM process using a resin inlet being a line source and having a helical coil positioned on the top of the peel ply or release film. This speeds the resin flow to the preform. The vacuum outlet is a line outlet positioned around the circumference of the preform for drawing the resin through the preform from a resin inlet centrally located over the preform. Different distribution media are also shown that aid in the uniform distribution of resin into the preform.
U.S. Pat. No. 5,052,906 by inventor Seemann and having the same title as the above discloses a VARTM apparatus having multiple resin inlets and having a vacuum line source on the opposite side of the preform and further also having a distribution medium layer on the top and bottom of the preform. Various types of distribution medium layers are disclosed.
U.S. Pat. No. 5,316,462 by inventor Seemann entitled “Unitary Vacuum Bag for forming Fiber Reinforced Composite Articles” discloses a means of impregnating a fibrous preform by using a bag system with a resin distribution conduit and the distribution medium formed as an integral part of the vacuum bag. The distribution medium is formed as an integral part of the lower surface of the vacuum bag. A vacuum conduit runs around the circumference of the preform and is a part of the mold.
The following U.S. patents are incorporated by reference: U.S. Pat. Nos. 4,902,215; 5,052,906; 5,134,002; 5,226,997; 5,316,462; and 5,588,392.
Thus, there exists a need for an improved VARTM process and apparatus for providing a means for improved dimensional tolerances and strength by having an increased volume fraction of fibrous materials.